Robert Harkness, Esq., on Fossil Footprinfs. 259 



this perhaps arises from the porous nature of this sub- 

 stance, as well as from the action of oxide of iron ; for the 

 arrangements of the particles in these deposits are such as 

 to allow free access, both of atmospheric air and also of 

 moisture, which would soon obliterate all traces of these 

 organisms ; while in deposits, where they have been rapidly 

 covered with mud or any substance impervious to air, these 

 would remain little changed, and capable of furnishing infor- 

 mation concerning the creatures of which they formed a 

 part. 



Had it not been for ichnolite impressions we should have 

 been induced to conclude that the presence of reptiles in for- 

 mations anterior to the lias was so rare that these animals 

 existed only to a small extent. With regard to chelonia, 

 without footprints we should not have been aware of their 

 occurrence ; and when we reflect on the conditions necessary 

 for the receiving and retaining of tracks, as well as that such 

 tracks have been made only in a littoral zone, we must arrive 

 at the conclusion, that negative evidence, so far as regards 

 geological formations, will not enable us to say that certain 

 classes of animals had no existence, because we find neither 

 organic remains nor footprints. The nature of almost the 

 whole of the deposits which constitute the geological forma- 

 tions is such as to indicate that these have originated from 

 the sea, and it is rarely that in these marine beds anything 

 is met with to shew what was the nature or form of the in- 

 habitants of the land which was above the surface of the sea 

 during the dift'erent epochs. 



That dry land existed at an early period there can be little 

 doubt, and it is equally probable that this dry land had its 

 occupants as well as the waters of the ocean by which it was 

 Burrounded. What the nature of these occupants may have 

 ibeen during the time when the Variegated sandstone was being 

 deposited we have at present no means of an-iving at, except 

 that the land-tortoises, which have left the impressof their foot- 

 steps on this sandstone cropped the vegetation which clothed 

 the soil, and drank of water which drained from the surface 

 of this land. The recent discovery of a fossil tooth in the 

 ^trias, of a form shewing that its possessor must have been 



R 2 



